Question

A piece of graphite has a cross-sectional area of 10 mm². If its resistance is 0.1 Ω and its resistivity 10x10^-8 Ωm, its length is

Answer 1

Given:

$A=10*10^{-6}\rm m^2$

$R=0.1\:\Omega$

$\rho=10*10^{-8}\:\rm\Omega\cdot m$

The resistance

$$R=\rho\frac{l}{A}$$

Hence, the length of a wire

$$l=RA/\rho=0.1*10*10^{-6}/10*10^{-8}=10\:\rm m$$